The invention concerns a plain bearing for the transmission of high axial forces and large flexural moments with small relative movements between the co-operating bearing components and a wind power installation with such a plain bearing between its pylon-supported machine head and the pylon head.
Plain bearings involving the demand profile as specified above can be used for example as pivot bearings in cranes, certain leisure and pleasure installations and indeed wind power installations (as so-called azimuth bearings). In that respect, a structural problem arises out of the fact that, even in the case of a vertical rotary axis, the forces, both in the direction of an applied load and also in the lifting-off direction, have to be carried by the bearing.
To attain the object which derives therefrom, in its general aspect the invention provides that an annular rib arranged on one co-operating bearing component engages into an annular groove provided on the other co-operating bearing component. In this case the annular rib may be of both a rectangular cross-section and also an outwardly converging trapezoidal cross-section; it is advantageously provided with anti-friction linings on its free side faces and on its peripheral faces. The anti-friction linings can be omitted in the case of a trapezoidal rib cross-section.
In order to be able to more easily replace the anti-friction linings which are inevitably subjected to wear, a development of the invention provides that the anti-friction linings are subdivided segment-like and are fixedly but releasably connected to the rib.
In particular in such a case it can further be provided that one of the co-operating bearing components is subdivided segment-like and the segments are releasable individually from their composite assembly. In particular the annular rib which is fitted with the anti-friction linings can be subdivided into segments and can be of such a configuration/arrangement that it engages radially from the outside into the inwardly disposed annular groove. Then the annular rib segments with the anti-friction lining segments secured thereto can be gradually released (in the peripheral direction) from their composite assembly and their fixing to the load-bearing or supported component, and pulled radially outwardly, and inserted again after having been fitted with new anti-friction lining segments. It will be appreciated that replacement by a substitute rib member provided with new anti-friction lining segments is also possible.
It will be appreciated that all arrangements can also be respectively reversed. Thus, the anti-friction linings can also be arranged at the inside surfaces of the annular groove which is subdivided segment-like and which engages from the outside over the inwardly disposed annular rib. In addition the respective inwardly disposed component (annular rib or annular groove) can be subdivided into segments. Then however the outwardly diverging wedge shape of the segments is a hindrance in regard to their being pulled out inwardly. In that case therefore the segments are to be edged in parallel relationship and compensating elements are possibly to be provided between the segments carrying the anti-friction linings.
In order to make it easier to replace the segments, it is possible to provide power-operated means such as for example pneumatically or hydraulically piston-cylinder units between the co-operating bearing components, which simultaneously engage them only in the stationary condition and which are capable of lifting the co-operating bearing component which is bearing downwardly, with respect to the bearing component supporting same, so that the fixing of the segments can be released and they can be withdrawn. After they have been refitted, the fixing of the load-relief means, at least to one of the co-operating bearing components, is released again.
In its specific aspect the invention further concerns a wind power installation having a plain bearing of the above-described kind between a pylon-supported machine head and the pylon head, wherein provided between the pylon head and the machine head is a tracking drive for rotation of the machine head about the vertical axis of the pylon, in dependence on wind direction, wherein the plain bearing is adapted to guide the machine head in the radial and in the axial direction.
The rotary bearing which is generally referred to as an azimuth bearing makes it possiblexe2x80x94by means of the tracking drivexe2x80x94to adjust the rotor which receives the wind power, in such a way that, depending on the respective wind direction, the highest level of efficiency is achieved and in addition, when the installation is stopped, the loading on all components of the installation is kept as low as possible. Usually, the rotary bearing which must be of large diameter in high-output wind power installations comprises a rotary ball-type connection (DE 41 04 137 C2 and DE 196 29 168 C1). Because generally only slight movements are to be effected about the axis of the pylon in the tracking movement of the machine head but considerable loads have to be carried more specifically when relatively high wind speeds are involved, that results in considerable static or quasi-static pressures in relation to surface area, within the rotary ball-type connection. Added to that is the fact that naturallyxe2x80x94and usually advantageouslyxe2x80x94a rotary ball-type connection opposes only a low level of resistance to the rotary movement, which however in the case of the azimuth bearing has the result that the machine head is involved in a xe2x80x98nervous, jerkyxe2x80x99 backward and forward movement when the wind direction experiences rapid changes, for example when the wind is gusty; the attempt is made to remedy that by means of damped control of the tracking movement or also by using mechanical brakes (DE 41 04 137 C2, 196 29 168 C1 and 198 14 629 A1).
In comparison therewith, the plain bearing according to the invention is substantially better suited to carrying high forces when small movements are involved. In the present case however there is also the consideration that the sliding friction in the bearing produces a kind of natural damping of excessively hectic tracking movements. Still further: because the static friction which is opposed to the beginning of a tracking movement is always greater than the sliding friction which occurs after the static friction has been overcome, substantially irrespective of the material pairing involved, the tracking movement is entirely suppressed in the event of short-term and/or minor changes in wind direction.
In the state of the art, plain bearings have already been used as azimuth bearings for wind power installations, but only in relation to relatively small installations (Hau, xe2x80x98Windkraftanlagenxe2x80x99, [xe2x80x98Wind Power Installationsxe2x80x99], page 270). Their above-discussed control function is neither recognised therein, nor could it discernibly appear.
The plain bearing can carry vertical forces which occur in the axial direction both in the direction of an applied load and also in the lifting-off direction. The anti-friction linings can be both pinned and also glued to the annular rib. For inspection of the anti-friction linings and therewith the rotary bearing and If necessary for replacement of the anti-friction linings or the segments of the co-operating bearing components, the arrangement preferably has at least one closable maintenance opening in the machine head flange (which opening can be closed for example by a plug); by virtue of rotating the machine head, it is possible to check over and maintain the entire rotary bearing.
The anti-friction linings preferably comprise a metal-plastic composite with a steel back and a pimpled acetal copolymer bearing surface.
Lubrication of the plain bearing is effected from below upwardly by means of continuous lubrication cartridges; old grease is delivered to the exterior on the top side of the bearing, and collected. For that purpose, below the annular groove into which the annular rib engages with the anti-friction linings, a peripherally extending seal is fitted into the machine head flange, which seals off the gap with respect to the pylon head flange. At the top side, a sealing strip is fixed above the annular groove to the machine head flange in such a way that it bears with its free region on the top side of the pylon head flange.